Fuse device



Dec. 15, 1942. s. R. SMITH, JR

FUSE DEVICE F'iledv Oct 15, 1941 Patented Dec. 15, 1942 FUSE DEVICE Sidney R. Smith, Jr., Pittsfield, Mass., assgnor to General Electric Company, a corporation of New York Application October 15, 1941, Serial No. 415,053

Claims.

My invention relates to fuse devices and more particularly to improved fuses of the type having provision for preventing rupture of the fusible element by steep wave front voltages such as lightning surges.

It has been found desirable in some installations to provide a fuse which will not rupture when the circuit in which it is connected is subjected to steep wave front volt-ages but which will rupture upon the passage of power frequency current of predetermined duration or magnitude. For example, it is desirable to open the circuit through a lightning arrester in the event that it continues to pass current of power frequency after a discharge due to a voltage impulse such as a lightning surge. It is essential that the fuse blows only if the arrester passes several half cycles of power frequency current which is characteristic of an arrester after failure. When the arrester operates normally it will discharge impulse current which may be followed by power' frequency current that will not last longer than one-half cycle, since an arrester in good condition is expected to interrupt the power frequency current at the first zero point. Hence vthe fuse should not blow due to impulse curren-ts or due Ito power frequency currents of one or two half cycles duration. A circuit arrangement of this type is described and claimed in Patent 2,158,- 859-Horikoshi, dated May 16, l1939, and assigned to the same assignee as the present invention. In the copending application of MacCarthy and Brownlee, Serial No. 390,076, filed April 4, 1941, and assigned to the same assignee as the present invention, there are described and claimed structural embodiments of impulse protected fuse devices of a type suit-able for commercial application of the circuit disclosed in the Horikoshi patent. The present invention is in the nature of an improvement over the devices disclosed in the MacCarthy and Brownlee application.

It is, therefore, an object of the present invention to provide a new and improved impulse protected fuse device which is simple and relatively inexpensive to manufacture and which is, at the same time, reliable in operation.

For a further consideration 4of what I believe to be novel and my invention, attention is directed to the following description and the claims appended thereto, taken in connection with the accompanying drawing. In the drawing Fig. 1 is a longitudinal view in section of a fuse device embodying one form of the invention; Fig. 2 is a schematic representation of the circuit employed in the fuse devices constructed in accordance with the present invention, and Fig. 3 is a longitudinal view in section of a modification.

In the embodiment illustrated in Fig. 1 an elongated cylindrical tube I0 of suitable insulating material, such as fiber, is externally threaded at its opposite ends for the reception of conducting sleeves II and I2. The tube Ill is also provided with opposed longitudinal slots or recesses I3 extending inwardly from one end thereof for the reception of a transverse supporting member I4 of good conducting material, such as a piece of copper tubing. |The member I4 provides a support for one end of the fusible element l5 and associated strain wire I6 which extend longitudinally of the tube I0 and terminate in an electrode at the lower end of :the tube. The electrode may comprise a conducting sleeve I1 which is swaged onto the lower end -of the strain wire I6, fusible elemen-t I5 and a flexible stranded conductor I8 which provides one terminal of the fuse device. The electrode also includes a flanged collar I9 which ts into the lower end of the tube I0 and cooperates with an inner surface of the lower conducting sleeve I2 to provide the electrodes of an arc gap which functions in a manner to be described more in detail at a later point in the specification. A suitable tab, 19a, may be provided on the collar I9 for preventing relative rotation of tube I0 and collar I9. A coil spring 2U is interposed between the collar I9 and a shoulder 2l on the inside vof the tube I0 to provide means for expelling the collar I9 and conductor I8 from the tube I0 upon the rupture of the fusible element I5 and associated strain wire I6.

As mentioned earlier in the specification, an inductive element is provided in series with the fusible element to provide a high impedance to steep wave front voltages. In the embodiment lof Fig. 1 an inductive winding or coil 22 is positioned on the tube I0 between the sleeves II and I2. One :terminal of the coil is connected to the sleeve I2 by a suitable binding screw 23 while the other terminal of the coil passes through the slot I3 of the tube I Il and is received within the end of the copper tube I4 which may be compressed upon .the coil end to form a good electrical connection as shown at I4a. The fusible element and strain wire are preferably soldered to the copper tube to complete lthe electric circuit from the sleeve I2 through the inductive winding, tube I4, fusible element I5 to the electrode comprising sleeve I'I and collar I 9.

In order to render the fuse device mechanically strong and reasonably weatherproof the coil 22 is mounted and protected in a novel manner.

As shown, the coil 22 is positioned within an annular insulating member 24 having a U-shaped cross section and is spaced between the conducting sleeves Il and I2 by insulating washers 25 and 26. Between the upper sleeve Il and the coil there is also interposed a conducting member 21 and a projecting casing 23 of conductive material. The conducting member 2l is in the form of a ring or washer having an extending portion 29 connected to the lower sleeve I2 by means of the binding screw 23. The casing 23 is in the form of an open-ended cylinder and the side wall conforms generally to the shape of the coil and extends in spaced relation thereto to provide a space which is filled with insulating' compound designated by numeral 3l) to form a reasonably weather-tight casing about the coil. The casing 28 may be formed of insulating material of good mechanical properties in which case provision must be made for electrically connecting member II and sleeve I2 such as, for example, locating conducting member 21 outside the casing 28 so that it directly contacts sleeve Il. The sleeve II, secured to the upper end of the tube I0, is internally threaded at 3| to receive a suitable connector such as the grounding stud of a lightning arrester.

From the foregoing description it is apparent that one circuit from the sleeve Il is completed to the conductor I8 through conducting member 21 and sleeve l2, across an air gap to the collar I9 and associated sleeve I'I, and that a parallel path also extends from the sleeve II through member 21, coil 22, tube I4, the fusible element I and strain wire I6, and the sleeve I'I to the conductor I8. Thus we have a circuit between sleeve II and conductor I8 which is illustrated schematically in Fig. 2 and comprises an inductive element 32 and a fusible element 32a connected in parallel with a gap 33. A lightning arrester 34 and ground connection 33 have been shown in Fig. 2 to illustrate the application of the fuse device of the present invention as an isolator for a lightning arrester.

In accordance with the teachings of the aboveidentified Horikoshi patent, the inductive winding and the gap are designed so that for voltages of steep wave front, as compared to the voltages of normal line frequency, the winding 32 offers such high impedance that the gap 33 will break down and prevent rupture of the fuse. However, if power current continues to flow after the surge is discharged the impedance of winding 32 thereto is sufficiently low that the voltage across gap 33 will not maintain an arc thereacross and current is allowed to pass through fuse 32a to rupture the same to open the circuit between the sleeve II and the conductor I8. Such a device is of particular value for connection in circuit with a lightning arrester to isolate the same from the power circuit by opening the ground connection thereof in the event that the arrester continues to pass current of power frequency after a lightning discharge. It is not essential that the rupture of the fusible element and the resulting expulsion of the conductor I8 from the lower end of the tube interrupt the arc in all cases since this may be accomplished by other protective devices of the system and the isolation provided by the impulse protected device of the present invention may be utilized solely to isolate the lightning arrester, for example, when power is reapplied to the circuit.

In Fig. 3 I have shown a modiiication of my invention which is essentially the same as that CTI described in Fig. 1 with the exception that an expulsion tube has been provided at the lower end of the fuse tube in order that the device may be capable of interrupting the arc which is established upon rupture of the fusible element and associated strain wire. In Fig. 3 the same reference numerals as used in connection with Fig. l have been used to designate corresponding parts. In the arrangement of Fig. 3 the conducting sleeve I2 at the lower end of the tube I is extended to provide an internally threaded portion |241. for the reception of the externally threaded expulsion tube 36. Between tubes I0 and 36 the sleeve I2 is provided with an inwardly extending circuit flange 3I which cooperates with the sleeve I'I to provide an arc gap.

In the modification shown in Fig. 3 the collar is not provided on the sleeve II but is located at the lower end of the expulsion tube 36 on a sleeve 33 swaged on the conductor I8. The collar I9 fits the lower end of the tube 3G in the same manner as it fits tube IJ in the modication shown in Fig. l. The spring 2U is positioned between the collar I9 and a shoulder 33 formed in spaced relation to the collar on the inner surface of the expulsion tube 36.

The circuit between the sleeve I I and the conductor I8 of the arrangement shown in Fig. 3 is the same as that illustrated in Fig. 2 and described in connection with Figs. l and 2. In the operation of the modification shown in Fig. 3, however, the expulsion of the fuse from the tube 36 may be made effective to interrupt the arc established upon rupture of the fusible element and associated strain wire. n

The embodiments of the invention illustrated in Figs. 1 and 3 and described in the foregoing specification provide a compact arrangement of the elements utilized for the impulse protected isolating fuse which is very compact and economical from a manufacturing standpoint, and which at the same time provides an isolator which is very acceptable from the standpoint of operation and reliability. When the conductor I8 and associated terminal are expelled from the lower end of the device it Serves as an indicator of the blown condition of the fuse and when connected in circuit with an arrester indicates a faulty arrester.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that changes and modiiications may be made without departing from my invention, and I, therefore, aim in the appended claims tocover all such changes and modications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A fuse device comprising in combination a tube of insulating material, a fusible element extending longitudinally of ysaid tube, an electrode electrically connected with one end of said fusible element, a conducting sleeve positioned on one end of said tube and having a portion thereof extending in spaced relation with respect to said electrode to provide a discharge gap, a conducting sleeve positioned on the other end of said tube and providing a line terminal for said device, an inductive winding surrounding said tube and positioned with respect thereto by said sleeves. means electrically connecting one end of said 4winding with both of `said sleeves, means electrically connecting the other end of said Winding and the end of said fusible element opposite said electrode, and conducting means associated with said electrode and providing a second line terminal of said device.

2. A fuse device comprising in combination, a tube of insulating material, a fusible element positioned in said tube, an inductive winding positioned on the exterior of said tube intermediate the ends thereof, a sleeve of conducting material secured to one end of said tube and electrically connected to one end of said inductive Winding and forming a line terminal of said device, a second sleeve of conducting material secured on the oppositie end of said tube and engaging said inductive winding to hold it assembled on said tube, an electrode electrically connected with one end of said fusible element, said last mentioned conducting sleeve cooperating with said electrode to form an arc gap in parallel with said fusible element and said inductive Winding.

3. A fuse device of the type providing an nductive element and a fusible element in series between a pair of lin-e terminals with a discharge gap in parallel with said series connected inductive element and fusible element comprising a tube of insulating material, a fusible element positioned Within said tube, a conducting sleeve positioned on one end of said tube and forming a line terminal of said fuse device, a conducting sleeve secured to the other end of said tube and forming one electrode of said discharge gap, an inductive winding positioned about said tube intermediate said sleeves, the inner ends of said sleeves providing opposed surfaces for positioning said coil and holding it in assembled relation on the exterior of said tube.

4. A fuse device comprising in combination a tube of insulating material having opposed longitudinal recesses extending inwardly from one end thereof, a supporting member positioned in said recesses extending transversely of said tube, a fusible element secured to said support and extending longitudinally of said tube, an electrode electrically connected with the other end of said fusible element and positioned adjacent one end of said tube, a sleeve of conducting material secured to the exterior of each end of said tube, one of said sleeves having a surface extending in spaced relation with said electrode and cooperating therewith to form an arc gap, and an inductive winding surrounding said tube and interposed between said sleeves, one end of said winding being electrically connected to one said sleeve and the other end of said Winding being electrically connected with the end of said fusible element attached to said support.

5. A fuse device comprising in combination a tube of insulating material, an inductive Winding surrounding said tube intermediate the ends thereof, a conducting sleeve secured to each end of said tube and providing means for maintaining said inductive winding in assembled relation with said tube, an enclosing casing for said inductive winding in the form of a cylinder having an opened end and a closed end apertured to receive said tube of insulating material, the end wall of said cylinder being engaged by one of said conducting members to hold said casing in position about said inductive winding, the side walls of said casing extending in spaced relation to the outer surface of said inductive winding and a layer of insulating compound interposed between said casing and said inductive winding for substantially sealing the open end of said casing, a fusible element housed Within said tube and extending longitudinally thereof, said element having one end electrically connected with one end of said inductive winding, an electrode electrically connected with the other end of said inductive winding and having a portion extending in spaced relation with one of said conducting elements to provide an arc gap, means electrically connecting the other end of said inductive winding with the other conducting sleeve, and conducting means conductively associated with said other electrode and forming a terminal element of said device.

SIDNEY R. SMITH, JR. 

